Magnetic speedometer.



ciZZ,uiLoinitniajI/concem: Be fit known-that-I, JOHN K.

y' UNITED ,mmv i; srnwaar, or cHIcaGo, 1'L I. 1-N,ors, assienoa'ro 'srEWnnT-'WARNnnsPi-inna omETEn conroniirron, ernennen-earn or vrasrmiay- STEWART, a

citizenl of' the-United States, Yresidingat C-.hicagmin-t-he county of @ook and State .of Illinoish ave invented new and useful '-Im' Whilrthe to-llon'ing 1 a specification, reference being vhad to 'the accompanying draw- A ings, forming apart thereof.

lThe purpose of this invention is to pro? 'vide an improved. form o't magnetic speedometer having means -for automatically com- 4pensating for errors due to temperature changes lt-consistsin the elements and vfeatures of .construction vshown and described as indicatedin the claims.

In the drawings :-'-Figure l is an axial sectiomat theline 1-1 on Fig. 2,- ot' Ian instr ument embodying this invention. Fig. 2

is a section at the line o'n Fig. l. Fig. 3 ,isa detail planview of the'inovable element and the means forumovingit. v

The instrument shown in the. drawingsis of familiar construction in the main features,

comprising [a ca se, 1, in' which there is mountedfo'r rotation a magnet carrier, 2, f lia-ving magnets mountedupon itjas herein-l after described, and, pivoted for oscillation about the axis'of the rotating magnet, a biased non-magnetic element, commonly called the drag element, 3, to whose spindle, 4, the indicator hand, 5, is attached for indi-v cating the speed of rotation. Upon the c'arrier,'2, there is mounted an outer pair lof f magn'ets, 8, 8, each semifannular in form and positioned Aco-'axially andsupplementally on the carrier, 9. ithin the outer magnets, 8,

y8, there is a second pair of semi-annular magnets, V6, 6', mounted co-axially upon the carrier, their diameters being such that a I "narrow annular'space isleft between them and the outer magnets, 8, 8, into which the ange, 3a, of the biased element, 3, depends, As shown, the poles of the tvvo pairs ofmag` nets 'are positioned opposite each other;-

'that is, the poles ofthe inner magnetare,

'substantially or nearly radially inward of opposite sign of the outer certain situations and uses tiis arrangetogether about the axis o f the carrier; and

MAGNETLC s PEEDoM-nrnnf spgciiiation orraersratent. Patented API-,1,1913 Application'tiled September 18, 1911. .Serial No. 649,816. v 'i i' to effect-such movement for. varyingthe magnetic drag to eompensateqfor theeffect of changes'fof temperaturegthere="`is con nected to thehub ofthe carrier onelend of a .curved bar', 9, of metal, having a high cofefficient of j expansion, the other'end being connected with the pair' of inner magnets, 6, 6, in anyconvenientmanneiy as forexv ample, by connection to one of said magnets as shown atl 9a inFig. 2."4The maximum eiiiciency, or efficacy lofthe .'magnets for producing eddy currents in the 'biased-element' is yobtained when the polesof the inner-mag-V thepoles 'of .the outer magnets. This position of maximum efiiciencyfmay be asceri tained with respect to any set of magnets-by .a little experiment, and the connection of netare at afcertain positionwith Irespect-to the. innermagnetsto the carrier by means of'the curved bar, 9 ,ivill 'be made so as to locate the poles at the point of.' maximum efficiency when the instrument is at the highest temperature at which it is designed tobe operated, because at suchhighes-t temperature .the resistance of the biased element is -f greatest, and the eddy currents -pi'oduced rtherein by a given magnetic `field rotating at.'

a given speed are least. Th'eproportions of the expanding and contracting bar, 9, ivill be made such' as to varythe position of the-v inner pair of magnets" with respect to the outer paiiby"therota'tive adj'ustn'ient described, the'necessary amount to compensate for the vchangein velectrical resistance of the biased element due to the change oftem` perature Within anypredetermined range for Which-the instrument is intended to be automatically compensated.

The two magnetsof each pair are shown arranged withtheir poles of the same sign ad]acent, -the two.- pairs .having their poles of opposite nam'e'opposedj to each other'with the biased drag element between them. When thus arranged, obviously the position of lstrongest drag action of the magnets upon the biased elenientfiswith the p oles of the inner pair directly inward from the poles air, and for ment of these severalmagnets is preferred.

as pair is not necessarily .limitedto tivo,

ybut in order to havethe magnets of each 'setv relatively positioned with respect to .their nog i poles, as' above described, that is, with .ad-

ljacent poles in every instancev ofthe saine .axially therewith with an annular interval between them, the drag element being positioned de ending intothe annular interval between t e paths' of rotation of said two magnets, said magnets being movable relatively to each other about the axis of the carrier-.to vary the relative positions of their respect-ive poles., and a thermostaticldevice mounted on the carrier and operating upon one of the t-wo magnets to rotatively move it relatively to the other by the'expansion and contraction of said thermostatic element.

' 2. In a magnetic speedometer, in combi-.

nation with a rotatable magnet carrier, a biased drag4 element mounted for oscillation about the axis of rotation. of .the carrier;I

two magnets mounted on the carrier, coaxially therewith,. with an annular interval i between their paths of rotation, the drag element being positionedl intruding into said interval, one of said 'magnets being movable about the axis of the carrier for a limited distance relatively to the other, to vary the relative position ofthe polesof the respective magnets, andv ay thermostatic device having one end fixed with respect to the carrier and the other end connected with the movable magnet for so moving it.

3. In a'magnetic speedometer, in combination with a rotatable magnet carrier; a biased'drag element mounted for oscillation about the axis of rotation of the carrier; two magnets mounted on the carrier coy axially therewith, with an annular interval between theni the drag element being positioned depending into the annular interval between the paths of rotation of said two magnets, one of said two magnets being movable' relatively to'the other for a limited distance about the .axis ofthe carrier to 'perature vary the relative positions of the poles of the. two magnets, and a thermostatic device attached at one end to the carrierand at the other end to the movable magnet for -so moving it responsive to the changes of tem- 4. In a magnetic speedometer, in combi nation with'a rotatable magnet carrier and biased drag element mounted for oscillation about the axis of rotat-ion. of the carrier; two sets of magnets, each set comprising an even number of magi ets mounted following each other in circnm erential order and occupying an ann-ular space, said magnets being pcsitioned in4 said annular. space with their respective poles of the same sign adjacent,

th-eftwo sets being 4relatively positioned on the carrier with the poles ofy one set opposite the poles of opposite sign of the other set, said two sets being co-axial and spaced apart from each other to leave an annular interval between them,the drag element being positioned depending into said annular interval.

5. In a magnetic speedometer, in combination with ay rotatable magnet carrier and a biased d 'ag element mounted for oscillation about the axis of rotationl of the carrier;

'two sets of magnets each set comprising an even number of magnets mounted following each other in circumferential order and occupying-an annular space, said inagnets being positioned in said annular 'space with their respectivepoles of the same sign adjacent, the two sets being relatively positioned on the carrier withv thelpoles of one .set opposite lthe' poles of opposite sign .of lthe other set, said twosets being co-axial and spaced apart from each other to leave an annular-interval between them, the drag element being positioned depending into said annularI interval; one of said sets being mounted on the carrier for a limited range of movement-'about the axis, and thermostatic means for so moving itwith changes of temperature.

In testimony whereof, I have hereunto set my hand at Chicago, Illinois, this 12th4 day of Septeinben-lQll. 1

JOHN K. STEVART.

Witnesses CHAs. S. BURTON, M. GERTRUDE ADY. 

